1. Field of the Invention
The present invention relates to a method of manufacturing a thin-film magnetic head having at least a magnetoresistive element for reading, and to a magnetoresistive device having a magnetoresistive element.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as surface recording density of hard disk drives has increased. Such thin-film magnetic heads include composite thin-film magnetic heads that have been widely used. A composite head is made of a layered structure including a recording head having an induction-type magnetic transducer for writing and a reproducing head having a magnetoresistive (MR) element for reading. MR elements include an anisotropic magnetoresistive (AMR) element that utilizes the AMR effect and a giant magnetoresistive (GMR) element that utilizes the GMR effect. A reproducing head using an AMR element is called an AMR head or simply an MR head. A reproducing head using a GMR element is called a GMR head. An AMR head is used as a reproducing head whose surface recording density is more than 1 gigabit per square inch. A GMR head is used as a reproducing head whose surface recording density is more than 3 gigabits per square inch.
Many of reproducing heads have a structure in which the MR element is electrically and magnetically shielded by a magnetic material.
Reference is now made to FIG. 21 to FIG. 26 to describe an example of a manufacturing method of a composite thin-film magnetic head as an example of a related-art manufacturing method of a thin-film magnetic head. This composite head incorporates a spin valve GMR element as a reproducing head. FIG. 21 to FIG. 24 are cross sections each parallel to the air bearing surface of the pole portion of the head.
According to the manufacturing method, as shown in FIG. 21, an insulating layer 102 made of alumina (Al.sub.2 O.sub.3), for example, and having a thickness of about 5.mu.m is deposited on a substrate 101 made of aluminum oxide and titanium carbide (Al.sub.2 O.sub.3 -TiC), for example. On the insulating layer 102 a bottom shield layer 103 made of a magnetic material and having a thickness of 2 to 3.mu.m is formed for a reproducing head.
Next, on the bottom shield layer 103, a first shield gap film 104a as an insulating layer made of an insulating material such as alumina is deposited to a thickness of 20 to 40 nm, for example, through sputtering. Next, a second shield gap film 104b as an insulating layer made of an insulating material such as alumina is deposited to a thickness of 50 to 150 nm, for example, through sputtering in a region on the first shield gap film 104a except where a GMR element described later is to be formed.
On the second shield gap film 104b a plurality of layers making up the GMR element for reproduction are formed. These layers are: an antiferromagnetic layer 105a having a thickness of about 10 to 20 nm; a nonmagnetic layer 105b having a thickness of about 2 to 3 nm; and a free layer (magnetic layer) 105c having a thickness of about 3 to 6 nm. These layers are formed in this order. In addition to these layers, layers such as a magnetic layer to be a pin layer may be required, if necessary, for making up the GMR element. However, the three layers 105a, 105b and 105c are only illustrated in the following description for simplification.
Next, on the free layer 105c a photoresist pattern 121 is selectively formed where the GMR element is to be formed. The photoresist pattern 121 is formed into a shape that facilitates lift-off, such as a shape having a T-shaped cross section.
Next, as shown in FIG. 22, with the photoresist pattern 121 as a mask, the above-mentioned layers 105a, 105b and 105c making up the GMR element are selectively etched through ion milling, for example, and patterned to form the GMR element 105.
Next, as shown in FIG. 23, using the photoresist pattern 121 as a mask, a pair of conductive layers (that may be called leads) 106 whose thickness is tens to a hundred and tens of nanometers, for example, are formed into specific shapes on the first shield gap film 104a and the second shield gap film 104b. The conductive layers 106 are electrically connected to the GMR element 105. Next, the photoresist pattern 121 is lifted off. FIG. 25 is a top view illustrating the second shield gap film 104b, the GMR element 105 and the conductive layers 106 at this point in the manufacturing steps.
Next, as shown in FIG. 24, a third shield gap film 107a made of an insulating material such as alumina and having a thickness of 20 to 40 nm, for example, is formed through sputtering, for example, as an insulating layer on the shield gap films 104a and 104b, the GMR element 105 and the conductive layers 106. The GMR element 105 is embedded in the shield gap films 104a and 107a. Next, a fourth shield gap film 107b made of an insulating material such as alumina and having a thickness of 50 to 150 nm, for example, is formed through sputtering, for example, as an insulating layer in a region on top of the third shield gap film 107a except the neighborhood of the GMR element 105.
Next, on the shield gap films 107a and 107b, a top-shield-layer-cum-bottom-pole-layer (called a top shield layer in the following description) 108 having a thickness of about 3.mu.m is formed. The top shield layer 108 is made of a magnetic material and used for both a reproducing head and a recording head.
Next, on the top shield layer 108, a recording gap layer 112 made of an insulating film such as an alumina film whose thickness is 0.2 to 0.3.mu.m is formed. Although not shown, a contact hole is formed through selectively etching a portion of the recording gap layer 112 in a center portion of a region where a thin-film coil described later is formed.
Next, although not shown, on the recording gap layer 112, a first photoresist layer for determining the throat height is formed into a specific shape whose thickness is about 1.0 to 2.0.mu.m. The throat height is the length (height) of portions of the two magnetic layers of the recording head between an end located in the air bearing surface (the medium facing surface that faces toward a recording medium) and the other end, the portions facing each other with the recording gap layer in between.
Next, on the first photoresist layer, the thin-film coil of the recording head is formed. The thickness of the coil is 3.mu.m, for example. Next, a second photoresist layer for insulating the thin-film coil is formed into a specific shape on the first photoresist layer and the coil. FIG. 26 is a top view illustrating the state at this point of the manufacturing steps in a simplified manner. In FIG. 26 numeral 113 indicates the thin-film coil illustrated in a simplified manner. Numeral 131 indicates conductive layers formed on ends of the conductive layers 106 farther from the GMR element 105. Numeral 132 indicates conductive layers connected to the conductive layers 131. The conductive layers 131 may be made of a material the same as that of the top shield layer 108 and formed at the same time as the top shield layer 108. The conductive layers 132 may be made of a material the same as that of the thin-film coil 113 and formed at the same time as the coil 113.
Next, as shown in FIG. 24, a top pole layer 114 having a thickness of about 3.mu.m is formed for the recording head on the recording gap layer 112 and the first and second photoresist layers. The top pole layer 114 is made of a magnetic material such as Permalloy (NiFe) and is in contact with and magnetically coupled to the top shield layer (bottom pole layer) 108 through the contact hole formed in the center portion of the region where the thin-film coil is formed.
Next, the recording gap layer 112 and a portion of the top shield layer (bottom pole layer) 108 are etched through ion milling, for example, using the top pole layer 114 as a mask. As shown in FIG. 24, the structure is called a trim structure wherein the sidewalls of the top pole layer 114, the recording gap layer 112, and a part of the top shield layer (bottom pole layer) 108 are formed vertically in a self-aligned manner. The trim structure suppresses an increase in the effective track width due to expansion of the magnetic flux generated during writing in a narrow track.
Next, an overcoat layer 115 of alumina, for example, having a thickness of 20 to 30.mu.m is formed to cover the top pole layer 114. Finally, lapping of the slider including the foregoing layers is performed to form the air bearing surface of the head including the recording head and the reproducing head. The thin-film magnetic head is thus completed.
As the performance of a reproducing head improves, a problem of thermal asperity comes up. Thermal asperity is a reduction in reproducing characteristics due to self-heating of the reproducing head during reproduction. To overcome such thermal asperity, a material having an excellent cooling efficiency has been sought for making the bottom pole layer and the shield gap films. The bottom pole layer is therefore made of a magnetic material such as Permalloy or Sendust in the prior art. Recently, a method has been taken, such as reducing the thickness of each shield gap film down to 20 to 50 nm, for example, in order to increase the cooling efficiency.
However, such thin shield gap films cause a problem that faults may result in the magnetic and electrical insulation that isolates the shield layers from the MR element (including the GMR element) or the conductive layers connected thereto.
In relation to this problem, another problem of the prior-art thin-film magnetic head is a short circuit between the shield layers and the MR element or the conductive layers connected thereto. This problem will now be described, referring to the example shown in FIG. 21 to FIG. 26.
In the method of manufacturing the thin-film magnetic head of the related art, as shown in FIG. 22, the layers 105a, 105b and 105c making up the GMR element are selectively etched through ion milling, for example, with the photoresist pattern 121 as a mask. The GMR element 105 is thus formed. The width and length of the GMR element 105 thereby defined determine the track width and the MR height (the length [height] of the MR element between the air-bearing-surface-side end and the other end) of the reproducing head. Therefore, over-etching is required to some extent when the layers 105a, 105b and 105c are etched through ion milling. Consequently, as shown in FIG. 22, the very thin first shield gap film 104a having a thickness of 20 to 40 nm may be damaged or etched and holes may be thus formed in the shield gap film 104a.
If the conductive layers 106 are formed, as shown in FIG. 23, while the first shield gap film 104a has holes, a short circuit is created between the bottom shield layer 103 and the conductive layers 106. Such a short circuit results in an increase in noise that affects the GMR element 105.
In Published Unexamined Japanese Patent Application Hei 7-296333 (1995), a technique is disclosed for making an insulating film in a region where the shield gap film is reduced in thickness because of ion milling for making the MR element. However, this technique will not reduce the damage itself to the shield gap film caused by ion milling.
In the related art, as shown in FIG. 22, an end of the geometry of the GMR element 105 is taper-etched. However, such taper-etching makes it more difficult to control the track width and the MR height with accuracy, as the track width and the MR height are reduced, in particular. Taper-etching is therefore one of the factors that reduce the yield.